On Mon, 20 Feb 2006, jori.hamalainen@??? wrote:
>
> Another note, changing file extension for mail transfer is easy (rename
> *.exe to *.ex_). File Id field (=file magic number) is harder to change
> (because you need to change it back at receiving side for the file to be
> usable), so probably you should scan it? So I ask should Exim have
> $filemagic variable (sorry if there already is)?
We used to use MailScanner's facilities for rejecting email based on the
output of the Unix file command. It had too many false positives, so we
stopped using it. It doesn't actually provide much extra safety: what we
are trying to protect against is malicious code, which generally takes the
easy route to infect a computer. Our policy isn't a blanket ban on
executables in email - we allow our users to send them in zip files, for
example - so renaming the file to work around the policy demonstrates that
the sender is unlikely to have criminal intent, so we might as well let it
through.
Tony.
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